Population Pharmacokinetic Study of Amoxicillin-Treated Burn Patients Hospitalized at a Swiss Tertiary-Care Center

The objective of this study was to investigate the population pharmacokinetics (PK) of amoxicillin in ICU burn patients and the optimal dosage regimens. This was a prospective study involving 21 consecutive burn patients receiving amoxicillin. PK data were analyzed using nonlinear mixed-effects modeling. Monte-Carlo simulations assessed the influence of various amoxicillin dosage regimens with identified covariates on the probability to achieve a target (PTA) value of time during which free amoxicillin concentrations in plasma exceeded the MIC (fT> MIC). A two-compartment model best described the data. Creatinine clearance (CLCR) and body weight (BW) influenced amoxicillin CL and central volume of distribution (V-1), respectively. The median CLCR (Cockcroft-Gault formula) was high (128 ml/min), with 25% of patients having CL(CR)s of >150 ml/min. The CL, V-1, and half-life (t(1/2)) values at steady state for a patient with a CLCR of 110 ml/min and BW of 70 kg were 13.6 liters/h, 9.7 liters, and 0.8 h, respectively. Simulations showed that a target fT > MIC of >= 50% was achieved (PTA > 90%) with standard amoxicillin dosage regimens (1 to 2 g every 6 to 8 h [q6 - 8h]) when the MIC was low (<1 mg/liter). However, increased dosages of up to 2 g/4 h were necessary in patients with augmented CL(R)s or higher MICs. Prolonging amoxicillin infusion from 30 min to 2 h had a favorable effect on target attainment. In conclusion, this population analysis shows an increased amoxicillin CL and substantial CL PK variability in burn patients compared to literature data with nonburn patients. Situations of augmented CLCR and/or high bacterial MIC target values may require dosage increases and longer infusion durations.